A vehicular air conditioning system used in an EV, a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like is unable to perform a heating operation using combustion exhaust heat of engine cooling water and the like. As such, a heat-pump-type air-conditioning system using an electric compressor is being considered. However, in a situation involving a reverse-type heat pump, various pipes and heat exchangers such as evaporators, condensers, and the like making up a refrigerant circuit must be able to operate jointly under different pressure conditions for cooling operation and heating operation. Thus, a current vehicular air conditioning system applicable to an engine-driven vehicle must be completely modified.
As such, a heat-pump-type vehicular air-conditioning system configured with a heating refrigerant circuit, where a cooling refrigerant circuit of a current system is used as is, with the addition of an onboard condenser (also termed a subcondenser) provided within a heating ventilation and air conditioning unit (hereinafter, HVAC unit) and of an external evaporator to the circuit via a switching valve, a bypass circuit, and the like, has been provided, for example by Patent Document 1.
Conversely, Patent Document 2 discloses a heat-pump-type vehicular air-conditioning system configured with a heating bypass circuit connected to an external condenser via a four-way valve and connected to a subcondenser on an upstream side of an expansion valve, with an evaporator disposed on a downstream side of the subcondenser within an HVAC unit. In addition, Patent Document 3 discloses a heat-pump-type vehicular air-conditioning system configured with an evaporator on an upstream side and an onboard condenser connected via an expansion valve on a downstream side disposed within an HVAC unit, uses two four-way valves on a refrigerant inlet side of the onboard condenser, is connected to a discharge side of a compressor via a vehicle-mounted external heat exchanger functioning as one of a condenser and an evaporator or via a bypass circuit thereof, and has a refrigerant outlet side of the evaporator connected to an inlet side of the compressor by the two four-way valves via the vehicle-mounted external heat exchanger or via the bypass circuit thereof.